I've seen two in my life. One in Daytona Beach a year or so ago during Bike Week. The other was three weeks ago in Germany. Both times I thought cool bike, bad sound. Real bad sound, like the bastard child of a popcorn machine and a blender with bad bearings.
While not the coolest bike in the world, I woudl suggest the SV650 for the wife bike/track bike combo. Tons of aftermarket race parts and easier/cheaper to fix if you crash it on the track.I would say that Prillia would have expensive parts on it if they needed to be replaced.
i had a little pocket racer with a 49cc engine in it. i ran the bike open HEAD and it was loud as fuck. imagine a weedwacker going off in your ear. mine did over 30mph stock and was perdy fast considering i was over 220 when i had it.
i would buy a yamaha zuma that would be fun for around town. i dont know why i think those are so cool.